8000 gh-135853: add `math.signbit` (#135877) · python/cpython@42ccac2 · GitHub
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gh-135853: add math.signbit (#135877)
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‎Doc/library/math.rst

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@@ -59,6 +59,7 @@ noted otherwise, all return values are floats.
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:func:`isnan(x) <isnan>` Check if *x* is a NaN (not a number)
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:func:`ldexp(x, i) <ldexp>` ``x * (2**i)``, inverse of function :func:`frexp`
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:func:`nextafter(x, y, steps) <nextafter>` Floating-point value *steps* steps after *x* towards *y*
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:func:`signbit(x) <signbit>` Check if *x* is a negative number
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:func:`ulp(x) <ulp>` Value of the least significant bit of *x*
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**Power, exponential and logarithmic functions**
@@ -431,6 +432,15 @@ Floating point manipulation functions
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Added the *steps* argument.
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.. function:: signbit(x)
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Return ``True`` if the sign of *x* is negative and ``False`` otherwise.
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This is useful to detect the sign bit of zeroes, infinities and NaNs.
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.. versionadded:: next
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.. function:: ulp(x)
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Return the value of the least significant bit of the float *x*:

‎Doc/whatsnew/3.15.rst

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@@ -115,6 +115,9 @@ math
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* Add :func:`math.isnormal` and :func:`math.issubnormal` functions.
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(Contributed by Sergey B Kirpichev in :gh:`132908`.)
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* Add :func:`math.signbit` function.
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(Contributed by Bénédikt Tran in :gh:`135853`.)
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os.path
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-------

‎Lib/test/test_math.py

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@@ -475,6 +475,19 @@ def testCopysign(self):
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# similarly, copysign(2., NAN) could be 2. or -2.
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self.assertEqual(abs(math.copysign(2., NAN)), 2.)
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def test_signbit(self):
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self.assertRaises(TypeError, math.signbit)
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self.assertRaises(TypeError, math.signbit, '1.0')
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# C11, §7.12.3.6 requires signbit() to return a nonzero value
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# if and only if the sign of its argument value is negative,
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# but in practice, we are only interested in a boolean value.
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self.assertIsInstance(math.signbit(1.0), bool)
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for arg in [0., 1., INF, NAN]:
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self.assertFalse(math.signbit(arg))
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self.assertTrue(math.signbit(-arg))
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def testCos(self):
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self.assertRaises(TypeError, math.cos)
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self.ftest('cos(-pi/2)', math.cos(-math.pi/2), 0, abs_tol=math.ulp(1))
@@ -1387,7 +1400,6 @@ def __rmul__(self, other):
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args = ((-5, -5, 10), (1.5, 4611686018427387904, 2305843009213693952))
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self.assertEqual(sumprod(*args), 0.0)
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@requires_IEEE_754
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@unittest.skipIf(HAVE_DOUBLE_ROUNDING,
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"sumprod() accuracy not guaranteed on machines with double rounding")
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with self.assertRaises(ValueError):
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math.nextafter(1.0, INF, steps=-1)
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@requires_IEEE_754
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def test_ulp(self):
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self.assertEqual(math.ulp(1.0), sys.float_info.epsilon)

‎Misc/NEWS.d/next/Library/2025-06-24-10-23-37.gh-issue-135853.6xDNOG.rst

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:mod:`math`: expose C99 :func:`~math.signbit` function to determine whether
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the sign bit of a floating-point value is set. Patch by Bénédikt Tran.

‎Modules/clinic/mathmodule.c.h

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‎Modules/mathmodule.c

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@@ -1233,6 +1233,23 @@ FUNC2(remainder, m_remainder,
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"Return x - n*y where n*y is the closest integer multiple of y.\n"
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"In the case where x is exactly halfway between two multiples of\n"
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"y, the nearest even value of n is used. The result is always exact.")
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/*[clinic input]
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math.signbit
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x: double
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/
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Return True if the sign of x is negative and False otherwise.
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[clinic start generated code]*/
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static PyObject *
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math_signbit_impl(PyObject *module, double x)
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/*[clinic end generated code: output=20c5f20156a9b871 input=3d3493fbcb5bdb3e]*/
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{
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return PyBool_FromLong(signbit(x));
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}
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FUNC1D(sin, sin, 0,
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"sin($module, x, /)\n--\n\n"
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"Return the sine of x (measured in radians).",
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MATH_POW_METHODDEF
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MATH_RADIANS_METHODDEF
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{"remainder", _PyCFunction_CAST(math_remainder), METH_FASTCALL, math_remainder_doc},
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MATH_SIGNBIT_METHODDEF
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{"sin", math_sin, METH_O, math_sin_doc},
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{"sinh", math_sinh, METH_O, math_sinh_doc},
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{"sqrt", math_sqrt, METH_O, math_sqrt_doc},

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